For example, the image-forming device disclosed in Japanese Patent Application Publication No. 2005-257813 is provided with a receptacle for collecting developer not transferred onto the recording sheet (waste toner). Specifically, this image-forming device supplies a motive force to a screw shaft used to convey waste toner via a slipper clutch, whereby the slipper clutch interrupts the transfer of the motive force to the screw shaft when torque greater than a prescribed amount is applied to the screw shaft. An encoder that rotates together with the screw shaft detects the rotating speed of the screw shaft.
As the amount of waste toner accumulated in the receptacle increases, the rotational force for rotating the screw shaft is increased. When the slipper clutch interrupts the transfer of the motive force, reducing the rotating speed of the screw shaft, it is determined that the amount of toner accumulated in the receptacle has exceeded a prescribed amount, indicating chat the receptacle should be replaced.